Simple optical sights (also colloquially known as “iron sights”) have long been used to aim firearms. Iron sights typically have two components: a rear sight that is between the user and the front sight, and a front sight that is between the rear sight and the opening at the end of the firearm barrel. One configuration of an iron sight is an “open sight” that includes a notch formed in the rear sight. This notch is aligned with a post on the front sight, both of which are aligned with a target to aim the firearm. An “aperture sight” is similar to the open sight except a circular hole is used as a rear sight, rather than a notch.
Some iron sights include mechanisms to adjust one or both of the rear sight and the front sight. These adjustment mechanisms can improve the aiming accuracy of the firearm for situations in which there is a difference in elevation between the firearm user and the target, or for situations in which wind may affect the trajectory of a fired projectile. However, regardless of whether or not an iron sight includes mechanisms to make these adjustments, iron sights are often integrated with (i.e., not removable from) the firearm.